Over the last decade, wireless communication services have been expanded. To provide such services, components of communication equipments have been complicated and large. It is therefore demanded to provide small size wireless communication equipments. In current smart antenna systems, a phase shifter is one of the main components, and is one of the limiting factors for reducing the size and required cost of the smart antenna systems.
The current phase shifters are categorized into a DSP phase shifter and a passive phase shifter. The DSP phase shifter converts received digital signals into digital form and performs phase shifting and power combining. The Power consumption in this approach is, however, high, and it requires off-chip components and silicon area. The passive phase shifters are expensive and cannot be integrated in a single chip.
Ellinger et al. discloses an adaptive antenna receiver in “An Antenna Diversity MMIC Vector Modulator for HIPERLAN with Low Power Consumption and Calibration Capability (IEEE Transactions on Microwave theory and techniques, Vol. 49, No. 5, May 2001)”. FIG. 1 shows the vector modular 200 of Ellinger et al. The vector modular 200 includes three paths 201, 202 and 203. For each path, a preamplifier is provided. In the paths 201-203, a lowpass filter 204, a capacitor 205 and a highpass filter 206 are provided. The gate nodes of three transistors E50 are connected to the lowpass filter 204, the capacitor 205 and the highpass filter 206, respectively. An input signal is applied to the preamplifiers, then to the paths 201-203 and is transmitted to the transistors E50. The vector modulator 200 achieves 360° phase shift.
However, the vector modulator 200 uses multiple pre-amplifiers and multiple inductors. That may result in higher noise and no-linearity of phase shifting, and then result in high cost if it is implemented in silicon. Further, matching circuit is not used between the two amplifiers. That may result in loss, higher noise and higher power consumption.
Therefore, it is desirable to provide a new phase shifter, which can meet demands for a small size and low cost, and can be integrated in a single chip with applications.